A fin tube heat exchanger is composed of a plurality of fins arranged at a predetermined distance, and a heat transfer tube penetrating the plurality of fins. Air flows between the fins, and exchanges heat with fluid inside the heat transfer tube.
FIGS. 9A to 9D are, respectively, a plan view of a fin in a conventional fin tube heat exchanger, a sectional view taken along line IXB-IXB, a sectional view taken along line IXC-IXC, and a sectional view taken along line IXD-IXD.
Fin 10 is shaped such that peak portion 4 and trough portion 6 appear alternately in the air stream direction. Such a fin is generally referred to as “corrugated fin.” The use of the corrugated fin makes it possible to obtain not only the effect of increasing a heat transfer area, but also the effect of thinning a temperature boundary layer by allowing air stream 3 to be serpentine.
FIGS. 10A to 10C are, respectively, a plan view of another fin in the conventional fin tube heat exchanger, a sectional view taken along line XB-XB, and a sectional view taken along line XC-XC. As illustrated in FIGS. 10A to 10C, a technique has been known in which the corrugated fin is provided with cut-and-raised portions to improve heat transfer performance (Patent Literature (hereinafter, referred to as “PTL”) 1).
Fin inclined surfaces 42a, 42b, 42c and 42d of fin 1 are provided with portions raised by cutting (hereinafter, referred to as “cut-and-raised portions”) 41a, 41b, 41c and 41d. When the distance between adjacent fins 1 is set as Fp, the respective heights H1, H2, H3 and H4 of cut-and-raised portions 41a, 41b, 41c and 41d satisfy the relationship: 1/5·Fp≦(H1, H2, H3, H4)≦1/3·Fp.
PTL 1 also discloses another fin configured to reduce the ventilation resistance during frost formation operation as much as possible. FIGS. 11A to 11C are, respectively, a plan view of yet another fin in the conventional fin tube heat exchanger, a sectional view taken along line XIB-XIB, and a sectional view taken along line XIC-XIC.
As illustrated in FIGS. 11A to 11C, fin inclined surfaces 12a and 12b of fin 1 are provided with cut-and-raised portions 11a and 11b which satisfy the above-mentioned relationship. Since fin 1 is bent fewer times, the inclination angles of fin inclined surfaces 12a and 12b are relatively gentle.